1. Field of the Invention
This invention relates to a method and device for electrical upsetting, that is, expanding to increase the diameter of the end part of metal raw material such as rods, pipes, and the like, in the main, by resistive heat generation at that part to soften.
2. Description of Prior Arts
The electrical upsetting method which has so far been in practice comprises the following four steps, in reference to FIGS. 1A through D of the accompanying drawing, wherein a reference numeral 1 designates a cylindrical shaping die for the upsetting work, a numeral 2 refers to a reinforcing ring for the shaping die 1, a numeral 3 denotes a die holder, 4 designates an anvil electrode having an electrode tip 41 at its distal end and also serving as a knock-out rod, 5 indicates a bushing to guide the forwarding and retracting movements of the anvil electrode 4, and 6 refers to an electrode in a clamping type, for example, to contact with a workpiece W.
Step A: The anvil electrode 4 is forwarded to position its distal end part 41 at the entrance opening of the shaping die 1, and the end face of the workpiece W clamped by the clamp electrode 6 is butted to the abovementioned electrode tip 41.
Step B: Electric current is caused to flow across the anvil electrode 4 and the clamp electrode 6, and, as the anvil electrode 4 is being gradually retracted, the workpiece W is pushed into the shaping die 1 under a strong pressure, during which the end part W' of the workpiece becomes softened by heat generated to contact the inner peripheral surface of the shaping die 1.
Step C: The workpiece W is further pushed into the die 1 until the electrode tip 41 reaches the bottom (or the innermost) part of the shaping die 1, when the upsetting work is terminated.
Step D: The clamp electrode 6 is released from the workpiece W, and the anvil electrode 4 is forwarded to thereby knock out the thus upset workpiece W from the shaping die 1.
In more detail, the end part W' of the workpiece increases its diameter and upset during the abovementioned steps B and C to contact the inner peripheral surface of the shaping die 1, and slide-moves along the contacted surface. In this case, the inner peripheral surface of the shaping die 1 for shaping the end part W' of the workpiece W, which has been softened by heat generation into an intended or predetermined shape is brought to a high temperature condition along with heating of the workpiece W, and is also subjected to vigorous frictional force with the result that it tends to be readily worn out. As the consequence of this, the service life of the shaping die 1 is generally short, and frequent exchange of the part is unavoidable. On account of this, a number of spare shaping dies have to be provided beforehand in preparation for such exchange.
Moreover, since the inner peripheral surface of the shaping die is more or less exposed to the external atmosphere, or air, it tends to be readily oxidized, which accelerates wear and tear in a rather short period of service.